Titanium nitride is a known barrier material used to prevent spiking of aluminum contacts into a silicon substrate. Titanium nitride can be deposited by sputtering titanium in the presence of argon and nitrogen gas. It is also known to enhance the barrier properties of titanium nitride by annealing or incorporating oxygen into the film. The oxygen fills the spaces between the grain boundaries of the titanium nitride. The annealing can be done in a Rapid Thermal Anneal (RTA) chamber or by heating in a nitrogen atmosphere containing oxygen. This is known as "stuffing" the titanium nitride layer. A layer of aluminum is deposited over the stuffed titanium nitride layer, also generally by sputtering. The aluminum layer can be heated then at temperatures above the flow temperature of aluminum to ensure that contact openings are completely filled.
As substrate wafer sizes become larger and devices made in the wafers become smaller and are placed closer together, many problems have arisen in filling small openings with material in a conformal manner that avoids the formation of voids. As the aspect ratio (width to depth ratio of openings) becomes higher, it becomes more difficult to fill openings, particularly by sputtering.
In an effort to improve the conformality of Ti/TiN. sputtered deposits, a collimator can be used in the sputtering chamber. This permits only vertically directed sputtered species to pass through the collimator to the substrate, thereby improving the conformality of the deposited films.
Liao et al disclosed an RTA treatment of a sputtered, low density titanium/titanium nitride stack, which formed a TiON layer at the titanium/titanium nitride interface. Their suggested process requires sputtering 550 .ANG. of titanium followed by sputtering 500 .ANG. of titanium nitride. The wafers are exposed to air and heated at 650.degree. C. in an RTA chamber after oxygen exposure of the titanium/titanium nitride stack. However, this process, although improving the barrier properties of the titanium/titanium nitride stack, requires a break in the vacuum after sputtering the titanium/titanium nitride layers to perform the oxygen exposure and RTA steps prior to sputter deposition of the overlying aluminum contact.
The above process works well, but requires extra oxygen exposure and annealing steps that reduce throughput, particularly for single wafer processing. Further, this process does not completely eliminate aluminum spiking. Thus the effort to improve titanium-containing barrier layers to prevent aluminum spiking through the layers to the substrate has continued.